The focal length of charged particle beams, such an electron beams, ion beams and the like, is usually controlled by an objective lens being fed by a control current. Prior art objective lenses are characterized by a relatively large response period. For example, the frequency response of a common objective lens has a cutoff at about 10 Hz. Accordingly; the objective lens cannot be utilized for fast changes of the focal length.
There is a need to provide a system and method for fast adjustment of the focal length of a charged particle beam.